An inkjet recording method is recently attracting attention. The inkjet recording method is a printing method of flying an ink composition in the form of small droplets and attaching it onto a recording medium such as paper, thereby performing the printing. This method is characterized in that a high-resolution and high-quality image can be printed at a high speed by using a relatively inexpensive apparatus. An inkjet recording apparatus utilizing this method is commercially accepted over a wide range by virtue of its print quality, low cost, relatively quiet operation and graphics capability. In particular, thermal (Bubblejet®) and piezoelectric drop-on-demand printers have succeeded on the market and have been widely used as a printer for personal computers in offices and homes.
In recent years, formation of a color image by inkjet recording is implemented by preparing a plurality of color ink compositions. In the formation of a color image, three colors of a yellow ink composition, a magenta ink composition and a cyan ink composition are generally used and depending on the case, four colors with the addition of a black ink composition are used. Furthermore, a color image is sometimes formed with six colors by adding a light cyan ink composition and a light magenta ink composition to the above-described four colors or with seven colors by further adding a dark yellow ink composition. The ink composition used for such formation of a color image is required not only to have good colorability by itself but also, for example, to produce a good intermediate color when combined with a plurality of ink compositions or cause no discoloration or fading of the printed matter during subsequent storage.
Also, by virtue of continuous improvements in respective fields of head, ink composition, recording method and media, the recent “photographic image quality” printing by a color inkjet printer has reached a level comparable to a “silver salt photography”, and the image quality has reached a “photographic quality”. Meanwhile, attempts to achieve characteristic enhancement by improving the ink composition and media are also being made on the preservability of the obtained image. Particularly, as for the light fastness, the characteristic enhancement to a level of causing no problem in practice has been achieved (see Patent Documents 1 and 2). However, the level is still not on a par with silver salt photography. In the standard evaluation of light fastness ability, the fading rate of each pure color pattern (optical density close to 1.0) of yellow, magenta and cyan is used as an index for the judgement. When the light fastness ability of the ink composition loaded in a printer currently available on the market is judged by this evaluation method, the ability of the magenta ink composition is lowest and in many cases, determines the light fastness life of an ink set. The improvement of light fastness of the magenta ink composition leads to enhancement of the light fastness of a photographic image and extension of the light fastness life of an ink set.
The printed matter prepared by using the above-described ink composition is disposed not only of course indoors but also sometimes outdoors and exposed to various lights (including sunlight) and outside airs (e.g., ozone, nitrogen oxide, sulfur oxide), and attempts are being made to develop an ink composition excellent in the fastness to light and gas. The properties such as light fastness and gas fastness are greatly governed by the coloring material in the ink, and development of a magenta ink composition excellent also in the moisture resistance in addition to these properties is being demanded.
Azo compounds described in Patent Documents 3 and 4 have been proposed as a colorant excellent in the light fastness and gas fastness.
Patent Document 1: JP 2000-290559 A
Patent Document 2: JP 2001-288392 A
Patent Document 3: JP 2002-371214 A
Patent Document 4: JP 2002-371079 A